At present, a common method in analyzing oil contents in rocks is by measuring chloroform extracted bitumen in rocks (see SY/5118-2005, Measurement of Chloroform extracted Bitumen in Rocks [S], Beijing, Standards Press of China, 2005). In the prior art, oil is extracted from rocks by using an organic solvent and through volatilizing the organic solvent to gain the oil weight by a balance. There exists three major drawbacks in this method: One is its limitation of accuracy of detection, because the method cannot detect an oil quantity with an absolute value of less than 0.001 g or an oil content less than 10 ppm; the other is that a portion of the oil volatilizes during the volatilization of the organic solvent, which may result in a lower measured value of the oil content; it is a more tedious procedure and usually takes a longer time to volatilize the solvent.